Liquid crystal display

ABSTRACT

A liquid crystal display comprises: first and second panels facing each other; a compensation film and a first polarizer disposed on the first panel, the compensation film having phase retardation characteristics; and a second polarizer having a supporting film disposed on the second panel, the supporting film having phase retardation characteristics. In alternative embodiments, a supporting film is used in place of the compensation film. The supporting film has retardation characteristics.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/474,759 filed on May 18, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/421,703 filed on Apr. 10, 2009, which is acontinuation of U.S. patent application Ser. No. 11/608,057 filed onDec. 7, 2006, which is a is a divisional of U.S. patent application Ser.No. 10/706,858 filed on Nov. 12, 2003, which claims priority to KoreanPatent Application No. 2003-0009354 filed on Feb. 14, 2003, thedisclosures of which are incorporated by reference herein in theirentireties.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure relates to liquid crystal displays, moreparticularly, liquid crystal displays having polarizing or compensatingfilms.

2. Discussion of the Related Art

A liquid crystal display (LCD) includes a pair of upper and lowerpanels, and a liquid crystal layer interposed therebetween for housingliquid crystals. The upper panel is provided with a common electrode andcolor filters; the lower panel is provided with pixel electrodes andthin film transistors (TFTs). The liquid crystals in the liquid crystallayer are subjected to an electric field generated between electrodes ofthe upper and lower panels. The variation of the field strength changesthe molecular orientations of the liquid crystals and the changedmolecular orientations in turn change the transmittance of light passingthrough the liquid crystal display such that desired images areobtained.

Light, an electromagnetic wave, oscillates in directions perpendicularto its moving direction. Generally, the oscillation of light is notconfined or biased to a particular direction. Thus, polarizers are usedto direct the transmitted light. Generally, polarizers are disposedexterior to the upper or lower panels such that the light transmittedthrough the liquid crystal layer is polarized.

A compensation film can also be interposed between the polarizer and theupper and lower panels to enhance viewing angle and/or color inversionfeatures of an LCD. The compensation film retards or shifts onecomponent of the light to convert the elliptically polarized lightgenerated by the liquid crystal display cell into linear polarizedlight, which can be effectively polarized by the polarizer.

Typically, a polarizer and a compensation film are separately disposedin an LCD, by affixing to the panel.

SUMMARY OF INVENTION

According to an embodiment of the present disclosure, a liquid crystaldisplay comprises: first and second panels facing each other; acompensation film and a first polarizer disposed on the first panel, thecompensation film having phase retardation characteristics; and a secondpolarizer having a supporting film disposed on the second panel, thesupporting film having phase retardation characteristics.

Preferably, the first polarizer includes a first supporting film and thephase retardation of the first supporting film combined with thecompensation film ranges about 130 nm to about 160 nm in the verticaldirection. The phase retardation of the second supporting film rangesabout 0 nm to about 5 nm in the horizontal direction and about 100 nm toabout 140 nm in the vertical direction. The phase retardation of thecompensation film ranges about 40 nm to about 60 nm in the horizontaldirection and about 80 nm to about 100 nm in the vertical direction, andthe phase retardation of the first supporting film ranges about 0 nm toabout 5 nm in the horizontal direction and about 50 nm to about 60 nm inthe vertical direction.

Preferably, an elongation direction for the polarizing medium havingzero value of phase retardation in the horizontal direction is the samedirection with an absorption axis of the polarizer disposed on the firstpanel. The compensation film is laminated perpendicular to theelongation direction of the polarizing medium.

Preferably, a liquid crystal layer for housing liquid crystalsinterposed between the first and the second panels. The liquid crystalsare aligned in a vertical alignment mode. The polarizers include apolarizing medium made of polyvinyl alcohol (PVA). The supporting filmsare made of triacetate cellulose (TAC) or cellulous acetate propionate(CAP).

According to another embodiment of the present disclosure, a liquidcrystal display comprises: first and second panels facing each other;and a first polarizer having a first supporting film disposed on thefirst panel and a second polarizer having a second supporting filmdisposed on the second panel, wherein the supporting films disposed onthe first panel and the second panel have phase retardationcharacteristics.

Preferably, phase retardation of the first supporting film ranges about40 nm to about 60 nm in the horizontal direction and about 120 nm toabout 160 nm in the vertical direction, and phase retardation of thesecond supporting film ranges about 0 nm to about 5 nm in the horizontaldirection and about 100 nm to about 140 nm in the vertical direction.

Preferably, the phase retardation of the first and second supportingfilms ranges about 40 nm to about 60 nm in the horizontal direction andabout 120 nm to about 160 nm in the vertical direction.

Preferably, the phase retardation of the first supporting film rangesabout 50 nm to about 70 nm in the horizontal direction and about 210 nmto about 250 nm in the vertical direction, and the phase retardation ofthe second supporting film ranges about 0 nm to about 5 nm in thehorizontal direction and about 50 nm to about 60 nm in the verticaldirection.

According to still another embodiment of the present disclosure, amethod of forming panels in a liquid crystal display device comprises:positioning first and second panels to face each other; disposing afirst polarizer having a first supporting film on the first panel; anddisposing a second polarizer having a second supporting film on thesecond panel, wherein the supporting films disposed on the first paneland the second panel have phase retardation characteristics.

According to another embodiment of the present disclosure, a method offorming panels in a liquid crystal display device comprises: positioningfirst and second panels to face each other; disposing a compensationfilm and a first polarizer on the first panel, the compensation filmhaving phase retardation characteristics; and disposing a secondpolarizer having a supporting film on the second panel, the supportingfilm having phase retardation characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more apparent by describing preferredembodiments thereof in detail with reference to the accompanyingdrawings, of which:

FIG. 1 is a sectional view of an LCD according to an embodiment of thepresent disclosure;

FIG. 2A shows an elongation direction of a polarizing medium;

FIG. 2B shows an elongation direction of a compensation film and asupporting film;

FIG. 3 is a sectional view of an LCD according to another embodiment ofthe present disclosure;

FIG. 4A shows an elongation direction of a polarizing medium;

FIG. 4B shows an elongation direction of a supporting film;

FIG. 5 is a sectional view of an LCD according to still anotherembodiment of the present disclosure;

FIG. 6A shows an elongation direction of a polarizing medium;

FIG. 6B shows an elongation direction of a supporting film; and

FIG. 7 is a sectional view of an LCD according to another embodiment ofthe present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present disclosure will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the disclosure are shown. This disclosure may, however, be embodiedin many different forms and should not be construed as being limited tothe embodiments set forth herein.

The liquid crystal displays according to embodiments of the presentinvention will now be described with reference to the drawings.

FIG. 1 is a sectional view of an LCD according to an embodiment of thepresent disclosure. As shown in FIG. 1, an LCD includes a lower panel110, an upper panel 210, and a liquid crystal layer 3 for housing liquidcrystals interposed between the lower panel 110 and the upper panel 210.The lower panel 110 includes a TFT array panel (not shown) and the upperpanel 210 includes a color filter (not shown). Alignment layers (notshown) are disposed on the two panels to anchor the liquid crystals.Electrodes (not shown) for generating electric field are formed on thetwo panels. The liquid crystals are preferably aligned in verticalalignment (VA) mode. In VA mode, the molecules of liquid crystals arenormally aligned at right angles to the panels, swinging through 90degrees to lie parallel with the panels in the presence of the electricfield.

A lower polarizer 12 is disposed under the lower panel 110. The lowerpolarizer comprises a polarizing medium 12 b interposed between twosupporting films 12 a and 12 c. As shown in FIG. 1, the supporting film12 c is positioned closer to the lower panel 110 as compared to thedistance between the supporting film 12 a and the lower panel 110.

A compensation film 23 is disposed on the upper panel 210 and an upperpolarizer 22 is disposed on the compensation film 23. The upperpolarizer 22 includes two supporting films 22 a and 22 c and apolarizing medium 22 b.

The supporting films 12 a, 12 c, 22 a, and 22 c are preferably made oftri-acetyl cellulous (TAC) or cellulous acetate propionate (CAP). Thepolarizing mediums 12 b and 22 b are preferably made of polyvinylalcohol (PVA).

The compensation film 23 is preferably formed as a thin film made of amaterial having different values for Nx, Ny, and Nz. Nx denotes therefractive index in the direction of its major axis. Ny denotes therefractive index in the direction of its minor axis. Nz denotes therefractive index in the direction perpendicular to the major and minoraxis.

Thin films such as the lower polarizer 12, the compensation film 23, andthe upper polarizer 22 exhibit phase retardation characteristics whichcan be used for enhancing viewing angle and/or color inversion. Phaseretardation of a thin film is calculated according to the followingequations:

$\begin{matrix}{{Ro} = {\left( {{Nx} - {Ny}} \right)d}} \\{R^{\prime} = {\left( {\frac{{Nx} + {Ny}}{2} - N_{z}} \right)d}}\end{matrix}$

Here, Ro denotes phase retardation in the horizontal direction. R′denotes phase retardation in the vertical (thickness) direction. Small ddenotes the thickness of the thin film.

According to an embodiment of the present disclosure, the supportingfilm 22 a can be made with Ro which is about 0 nm to about 5 nm and R′which ranges between about 50 nm and about 60 nm. The compensation film23 on the upper panel 210 can be made with Ro ranging between about 40nm and about 60 nm and R′ ranging between about 80 nm and about 100 nm.Thus, R′ of the thin film on the upper panel 210 in total ranges betweenabout 130 nm and about 160 nm. The supporting film 12 c of the lowerpolarizer 12 can be made with Ro which is about 0 nm to about 5 nm andR′ ranges between about 100 nm and about 140 nm. Having suchcharacteristics, the lower polarizer 12 increases phase retardation andadditional compensation films are not necessary under the lower panel110.

Thus, the same overall effect as was achieved in conventional art usingcompensation film is achieved by the lower polarizer 12 without usingcompensation film. Although description of the above embodiment isdirected to upper and lower polarizers, one ordinary skilled in the artcan readily appreciate that the upper and lower panels and associatedpolarizers and films are interchangeable, without degradation inretardation characteristics.

Thin films of zero (0) Ro, i.e., thin films having no phase retardationin their horizontal direction, can be fabricated by lamination using aroll. FIG. 2A shows an elongation direction for the polarizing medium 22b. FIG. 2B shows an elongation direction for the compensation film 21

As shown in FIGS. 2A and 2B, an absorption axis B of the upper polarizer22 along which the light vanishes is the same as an elongation directionA of the polarizing medium 22 b. A polarization axis (not shown) of theupper polarizer 22 along which the light penetrates is perpendicular tothe elongation direction A of the polarizing medium 22 b. A phaseretardation axis D of the compensation film 23 having non-zero value ofRo should be perpendicular to the absorption axis B of the upperpolarizer 22. Therefore, the compensation film 23 is preferablylaminated in the direction C perpendicular to the elongation direction Aof the polarizing medium 22 b.

FIG. 3 is a sectional view of an LCD according to another embodiment ofthe present disclosure. As shown in FIG. 3, an LCD includes a lowerpanel 110, an upper panel 210, and a liquid crystal layer 3 for housingliquid crystals interposed between the lower panel 110 and the upperpanel 210. The liquid crystals are preferably aligned in verticalalignment (VA) mode. A lower polarizer 12 is disposed on the lower panel110. The lower polarizer comprises a polarizing medium 12 b interposedbetween two supporting films 12 a and 12 c. The upper polarizer 22includes two supporting films 22 a and 22 c and a polarizing medium 22b.

The supporting film 22 a is preferably formed as a thin film made of amaterial having different values for Nx, Ny, and Nz. The supportingfilms 12 a, 12 c, and 22 c can be made of tri-acetyl cellulous (TAC) andthe polarizing medium 12 b and 22 b can be made of poly-vinyl alcohol(PVA). The supporting film 22 a can be made with Ro which ranges betweenabout 40 nm and about 60 nm and R′ which ranges between about 120 nm andabout 160 nm. The supporting film 12 c can be made with Ro which isabout 0 nm to about 5 nm and R′ which ranges between about 100 nm andabout 140 nm.

The lower polarizer 12 increases phase retardation because thesupporting film 12 c has R′ ranging between about 100 nm and about 140nm. The upper polarizer 22 increases phase retardation because thesupporting film 22 a has Ro ranging between 40 nm and 60 nm and R′ranging between about 120 nm and about 160 nm. Thus, a compensation filmis neither necessary under the lower panel 110 nor above the upper panel210.

FIG. 4A shows the elongation direction for the polarizing medium 22 b.FIG. 4B shows the elongation direction for the supporting film 22 a. Asshown in FIGS. 4A and 4B, an absorption axis B of the upper polarizer 22along which the light vanishes is the same as an elongation direction Aof the polarizing medium 22 b. A polarization axis (not shown) of theupper polarizer 22 along which the light penetrates is perpendicular tothe elongation direction A of the polarizing medium 22 b.

A phase retardation axis D of the supporting film 22 a having non-zerovalue of Ro is the same as an elongation direction C of the supportingfilm 22 a. The phase retardation axis of the supporting film 22 a havingnon-zero value of Ro should be perpendicular to the absorption axis B ofthe upper polarizer 22. The supporting film 22 a can be laminated in thedirection C perpendicular to the elongation direction A of thepolarizing medium 22 b.

According to still another embodiment of the present disclosure as shownin FIG. 5, the supporting film 12 c and the supporting film 22 a arepreferably formed as thin films made of a material having differentvalues of Nx, Ny, and Nz. The supporting films 12 a and 22 c can be madeof tri-acetyl cellulous (TAC) and the polarizing mediums 12 b and 22 bcan be made of poly-vinyl alcohol (PVA).

Both the supporting film 12 c and the supporting film 22 a can be madewith Ro which ranges between about 40 nm and about 60 nm and R′ whichranges between about 120 nm and about 160 nm. The lower polarizer 12increases its phase retardation because the supporting film 12 c has Roranging between about 40 nm and about 60 nm and R′ ranging between about120 nm and about 160 nm. The upper polarizer 22 increases its phaseretardation because the supporting film 22 a has Ro ranging betweenabout 40 nm and about 60 nm and R′ ranging between about 120 nm andabout 160 nm.

FIG. 6A shows the elongation direction for the polarizing medium 12 band the polarizing medium 22 b. FIG. 6B shows the elongation directionfor the supporting film 22 a and the supporting film 12 c.

As shown in FIGS. 6A and 6B, an absorption axis B of the upper polarizer22 along which the light vanishes is the same as an elongation directionA of the polarizing medium 22 b. A polarization axis (not shown) of theupper polarizer 22 along which the light penetrates is perpendicular tothe elongation direction A of the polarizing medium 22 b. An absorptionaxis B of the lower polarizer 12 along which the light vanishes is thesame as an elongation direction A of the polarizing medium 12 b. Apolarization axis (not shown) of the lower polarizer 12 along which thelight penetrates is perpendicular to the elongation direction A of thepolarizing medium 12 b.

A phase retardation axis D of the supporting film 22 a having non-zerovalue of Ro is the same as an elongation direction C of the supportingfilm 22 a. The phase retardation axis D of the supporting film 22 ahaving non-zero value of Ro should be perpendicular to the absorptionaxis B of the upper polarizer 22. A phase retardation axis D of thesupporting film 12 c having non-zero value of Ro is the same as anelongation direction C of the supporting film 12 c. The phaseretardation axis D of the supporting film 12 c having a non-zero valueshould be perpendicular to the absorption axis B of the upper polarizer22.

The supporting film 22 a can be laminated in the direction Cperpendicular to the elongation direction A of the polarizing medium 22b. The supporting film 12 c can be laminated in the direction Cperpendicular to the elongation direction A of the polarizing medium 12b.

FIG. 7 is a sectional view of an LCD according to still anotherembodiment of the present disclosure. As shown in FIG. 7, an LCDincludes a lower panel, an upper panel 210, and a liquid crystal layer 3for housing liquid crystals interposed between the lower panel 110 andthe upper panel 210. The liquid crystals are preferably aligned invertical alignment (VA) mode. A lower polarizer 12 is disposed on thelower panel 110. The lower polarizer comprises a polarizer medium 12 binterposed between two supporting films 12 a and 12 c. The upperpolarizer 22 includes two supporting films 12 a and 12 c. The upperpolarizer 22 includes two supporting films 22 a and 22 c and apolarizing medium 22 b.

The supporting film 22 a is preferably formed as a thin film made of amaterial having different values for Nx, Ny, and Nz. The supportingfilms 12 a, 12 c, and 22 c can be made of tri-acetyl cellulous (TAC) andthe polarizing medium 12 b and 22 b can be made of poly-vinyl alcohol(PVA). The supporting film 22 a can be made with Ro which ranges betweenabout 50 nm and about 70 nm and R′ which ranges between about 210 nm andabout 250 nm. The supporting film 12 c can be made with Ro which isabout 0 nm to about 5 nm and R′ which ranges between about 50 nm andabout 60 nm.

The lower polarizer 12 increases phase retardation because thesupporting film 12 c has R′ ranging between about 50 nm and about 60 nm.The upper polarizer 22 increases phase retardation because thesupporting film 22 a has Ro ranging between 50 nm and 70 nm and R′ranging between about 100 nm and about 140 nm. Thus, a compensation filmis neither necessary under the lower panel 110 nor above the upper panel210.

Elongation directions for the polarizing medium 22 b and the supportingfilm 22 a are the same with the embodiment described in connection withFIGS. 4A and 4B.

Although preferred embodiments of the present disclosure have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

What is claimed is:
 1. A liquid crystal display device, comprising:first and second panels facing each other; a first polarizer having afirst supporting film disposed on the first panel, a first polarizingmedium disposed on the first supporting film, and a second supportingfilm disposed on the first polarizing medium; and a second polarizerhaving a third supporting film disposed on the second panel, a secondpolarizing medium disposed on the third supporting film, and a fourthsupporting film disposed on the second polarizing medium, wherein thethird supporting film has a phase retardation of non-zero value in thehorizontal direction and in the vertical direction, and wherein thefirst, second and fourth supporting films comprise triacetate cellulose(TAC).
 2. The liquid crystal display device as in claim 1, furthercomprising a liquid crystal layer disposed between the first panel andthe second panel.
 3. The liquid crystal display device as in claim 2,wherein the liquid crystal layer is aligned in a vertical alignmentmode.
 4. The liquid crystal display device as in claim 3, wherein thethird supporting film is a thin film having different values for Nx, Ny,and Nz wherein Nx denotes the refractive index in the direction of majoraxis, Ny denotes the refractive index in the direction of minor axis,and Nz denotes the refractive index in the direction perpendicular tothe major and minor axis.
 5. The liquid crystal display device as inclaim 3, wherein the first and second polarizing mediums are made ofpolyvinyl alcohol (PVA).
 6. The liquid crystal display device as inclaim 5, wherein an elongation direction for the second polarizingmedium is substantially the same direction with an absorption axis ofthe second polarizer disposed on the second panel.
 7. The liquid crystaldisplay device as in claim 6, wherein an elongation direction for thethird supporting film is perpendicular to the absorption axis of thesecond polarizer disposed on the second panel.
 8. A method of formingpanels in a liquid crystal display device, comprising: positioning firstand second panels to face each other; disposing a first polarizer havinga first supporting film on the first panel, a first polarizing medium onthe first supporting film, and a second supporting film on the firstpolarizing medium; and disposing a second polarizer having a thirdsupporting film on the second panel, a second polarizing medium on thethird supporting film, and a fourth supporting film on the secondpolarizing medium, wherein the third supporting film has a phaseretardation of non-zero value in the horizontal direction and in thevertical direction, and wherein the first, second and fourth supportingfilms comprise triacetate cellulose (TAC).
 9. The method as in claim 8,further comprising disposing a liquid crystal layer between the firstand the second panels.
 10. The method as in claim 9, wherein the liquidcrystal layer is aligned in a vertical alignment mode.
 11. The method asin claim 10, wherein the third supporting film is a thin film havingdifferent values for Nx, Ny, and Nz wherein Nx denotes the refractiveindex in the direction of major axis, Ny denotes the refractive index inthe direction of minor axis, and Nz denotes the refractive index in thedirection perpendicular to the major and minor axis.
 12. The method asin claim 11, wherein the first and second polarizing mediums are made ofpolyvinyl alcohol (PVA).
 13. The method as in claim 12, wherein anelongation direction for the second polarizing medium is substantiallythe same direction with an absorption axis of the second polarizerdisposed on the second panel.
 14. The method as in claim 13, wherein anelongation direction for the third supporting film is perpendicular tothe absorption axis of the second polarizer disposed on the secondpanel.
 15. A liquid crystal display device, comprising: first and secondpanels facing each other; a first polarizer having a first supportingfilm disposed on the first panel, a first polarizing medium disposed onthe first supporting film, and a second supporting film disposed on thefirst polarizing medium; and a second polarizer having a thirdsupporting film disposed on the second panel, a second polarizing mediumdisposed on the third supporting film, and a fourth supporting filmdisposed on the second polarizing medium, wherein the third supportingfilm has a R₀ of non-zero value and a R′ of non-zero value, and whereinthe first, second and fourth supporting films comprise triacetatecellulose (TAC).